Developments of hydroponics designed to perform plant cultivation by soaking roots (underground parts) of plants in water without using soil are now in progress. Particularly in the case of root crops, surrounding conditions of roots are important factors in order to achieve good growth by the hydroponics. For example, high humidity at the roots may incur diseases or appropriate humidity management may promote growth of root hairs.
Techniques disclosed in the following PTL 1 and 2 have been known as techniques related to the hydroponics.
PTL 1 describes a method of promoting rapid growth of roots by realizing a highly humid condition. PTL 2 describes a technique to maintain a sufficient amount of moisture near roots by controlling an atomizer and an air controller using a signal from a dew sensor provided near a root holder.
However, the techniques described in the above-mentioned PTL 1 and 2 do not refer to environmental conditions at an underground part of a plant in a hydroponic cultivation apparatus.
In the meantime, the techniques described in PTL 1 and 2 state that it is desirable to establish a highly humid condition as a growth environment for a plant. Therefore, the techniques are not applicable to growing a plant body for which a highly humid condition is undesirable as its growth environment.
The present invention has been made in view of the aforementioned circumstances. An object of the present invention is to provide a hydroponic cultivation apparatus and a hydroponic cultivation method, which are capable of ameliorating an environment for an underground part of a plant.